Dylann Roof, who has been charged with the church shooting Charleston, S.C., is shown in a photo posted on a website authorities say was his.

Years ago, I took a journalistic excursion through the nation's white supremacist scene. I read books and spoke with professors, attended rallies with Aryan Nations members and Keystone Skinheads and interviewed their leaders. I kept in touch with the pre-eminent hate group watchdog, the Southern Poverty Law Center.

When I heard about Dylann Roof, I suspected that he had trod the same path.

The signs were familiar. Roof reportedly said to the nine African-Americans he shot point-blank inside a South Carolina church that he resented black men routinely raping white women -- a paranoid fiction long spread by white supremacists. Roof also said the shootings were meant to set off a "race war." White supremacists envision an armed battle leading to a breakaway, all-white, Gentile nation within the United States.

So, where did Roof acquire his racial hatred? At 21, he's lived in a post-civil rights era in a country that has never been so diverse.

He was active in an online white supremacist community. Roof started a site called The Last Rhodesian, a reference to apartheid-era southern Africa. He also may have posted as AryanBlood1488 on the DailyStormer.com, according to the Southern Poverty Law Center, which has identified 784 hate groups, from Klansmen to black separatists and border vigilantes.

We should consider whether people who run such websites bear some responsibility for the nine dead at Charleston's Emanuel African Methodist Episcopal Church. It would be difficult, but perhaps we should carve out an exception to our First Amendment protection of free speech to hold people accountable for hate speech.

We have harsher federal penalties for hate-motivated crimes, which Roof will presumably face. What about prosecuting those who inspired the action?

The digital world has raised the stakes since the Founding Fathers put their doctrines on paper. Now, instructions on building a bomb, the home address of an abortion doctor, or the location of a church at the heart of slavery resistance live online forever. They spread information across generations and at the click of a mouse.

What's more, these dangerous websites serve as live communities to validate people feeling outcast, unhappy and isolated. Hate speech doesn't cause someone to act against his will, of course, but it sets the stage for violence in which a sympathizer may even anticipate praise for taking action. According to news reports, Roof hesitated at the rear of the church as he listened to the prayer group, but then felt he must finish his mission to "kill black people."

Hate speech is illegal in Canada. The law bans exposing a person "to hatred or contempt . . . on the basis of a prohibited ground of discrimination" and to "willfully [promoting] hatred against any identifiable group."

That isn't the same as outlawing dissent. Hate speech as Canada defines it targets humans based on identity -- a skin color, a turban or walking to a temple on Saturday.

In 1990, the Canadian Supreme Court wrote that "hate propaganda can operate to convince listeners . . . that members of certain racial or religious groups are inferior," which can "increase acts of discrimination . . . and even incidents of violence."

In the United States, we prize our freedom to speak, but in fact our laws uphold many limits. Sedition, for example, or advocating force as a way to change the government, is illegal. Threats, defamation, false advertising and profanity on public airwaves are illegal. Companies protect trade secrets, and courts enforce gag orders in legal settlements.